This invention relates to an induction heating roller apparatus.
It is well known in the art that, in the case where sheet material such as plastic, paper, cloth, nonwoven cloth, and thin metal plate, or web material (hereinafter referred to merely as "a product", when applicable) is continuously hot-rolled, a pair of hot rollers called "hot calendar rollers, emboss rollers, or thermal bonding rollers" are used, or one hot roller and an elastic roller abutted against the hot roller are used to nip the sheet or web between those rollers.
In the operation thereof, it is required to uniformly apply a predetermined nip pressure to the sheet or web, and to uniformly heat it. In order to meet this requirement, the accuracy in heating temperature distribution in the axial direction of the roller, and the bending of the rollers by their own weight must be taken into account mainly. If it is assumed that a hot calendar roller having the outer diameter of 500 mm has a surface temperature difference of 10.degree. C., then the diameter has a thermal expansion difference of the order of 0.05 mm. That is, when the heating operation and the pressurizing operation are not uniform, there is a possibility that the quality of the resultant product is adversely affected. Hence, the surface temperature of the roller must be uniform in the direction of axis.
When a load is applied to the product to pressurize the product, the roller is bent by the load. The rotational axis of the roller thus bent is arcuate as viewed from the outside. As a result, especially near the middle of the roller in the direction of axis, a gap is formed between the pair of rollers. In this case, as well as the above-mentioned operation, the heating operation and the pressurizing operation are not uniform, so that there is a possibility that the quality of the resultant product is adversary affected. Hence, it is essential to prevent the roller from being bent by the load.
In a hot roller of this type, the above-described requirement is conventionally satisfied in such a manner that hot oil is utilized as its thermal source, and that so-called "crown roller" the middle portion of which is made arcuate so that it is larger than the end portions in correspondence to the amount of deflection is provided, or a means for applying an oil pressure to the inner cylindrical surface of the roller to amend the deflection is provided.
On the other hand, attention has been paid to an induction heating roller apparatus as the heating roller of this type which can be put in the production line because of its characteristics, quick heating, high-temperature heating, and contact-less heating. The induction heating roller apparatus in which the deflection of the roller generated by the load is amended, is disclosed in the Japanese Patent Unexamined Publication No. 12791/1990.
The induction heating roller apparatus thus disclosed will be briefly described with reference to a longitudinal sectional view of FIG. 1, and a cross sectional view of FIG. 2. A stationary shaft 2 is fixedly set on a stand 1, and a plurality of magnetic flux generating mechanisms 5 are mounted on the stationary shaft 2 at predetermined intervals in the direction of axis. Each of the magnetic flux generating mechanisms 5 comprises iron core 3 and induction coils 4. Hydraulic operating mechanisms 8 are respectively provided between the adjacent magnetic flux generating mechanisms 5 in the direction of axis. Each of the hydraulic operating mechanisms 8 comprises a piston 6 which is moved by oil pressure in the radial direction of the stationary shaft 2, and a cylinder 7 in which the piston 6 is inserted.
In addition, a roller 9 is rotatably supported on the stationary shaft 2. The roller 9 has jacket chambers 10 in its cylindrical wall in which two-phase (gas and liquid) heating medium is sealingly filled.
Since the induction heating roller apparatus is constructed as described above, when AC current is applied to the induction coils 4 of the magnetic flux generating mechanisms 5, alternating magnetic flux outputs are produced in magnetic circuits which are made up of the iron cores 3 of the magnetic flux generating mechanisms 5 and the cylindrical wall of the roller. Those alternating magnetic flux outputs go across the inner cylindrical wall of the roller 9, so that induction currents are generated therein. The Joule heat of the induction currents heats the inner cylindrical wall of the roller 9. In this operation, the two-phase (gas and liquid) heating medium in the jacket chambers 10 formed in the cylindrical wall of the roller 9 perform latent heat transfer, so that the surface temperature distribution of the roller 9 in the direction of axis is uniform.
In the hydraulic operating mechanisms 8, pressurized oil is supplied to the cylinders 7 through an oil path 13 formed in the stationary shaft 2, so that the pistons 6 are pushed towards the inner cylindrical wall of the roller 9, thereby to amend the deflection of the roller 9.
On the other hand, since the roller 9 rotates while the cylindrical wall of the roller 9 are being pushed by the pistons 6, an inner race 11 and rolling elements 12 such as rollers are provided between the end of each piston 6 and the inner cylindrical wall of the roller in order not to obstruct the rotation of the roller. That is, it is possible that the piston 6 is pushed against the inner race 11 to amend the deflection of the roller.
The conventional induction heating roller apparatus thus constructed is advantageous in that the temperature distribution of the roller in the direction of axis is uniform, and the deflection of the roller by the load applied thereto can be amended in the above-described manner.
However, it is still disadvantageous in the following points:
The arrangement of the hydraulic operating mechanisms is limited in density because the hydraulic operating mechanisms are arranged in the direction of axis between the magnetic flux generating mechanisms which are finely divided in the direction of axis. Accordingly, it is difficult to delicately amend the deflection of the roller. In addition, there is a fear of being adversely affected by the variation in diameter of the roller which is caused by "thermal crown" between the adjacent magnetic flux generating mechanisms, because the distance between adjacent magnetic flux generating mechanisms is relatively long. Moreover, the current allowed to flow in the induction coils is limited with respect to the size of the roller, so that it is impossible to increase the temperature of the roller, and to supply more thermal energy to the roller.